Spring之BeanFactoryPostProcessor详解

目录

功能与作用

使用案例

spring提供的常见BeanFactoryPostProcessor

1.EventListenerMethodProcessor

2.BeanDefinitionRegistryPostProcessor

功能与作用

使用案例

spring提供的唯一BeanDefinitionRegistryPostProcessor

总结

---

功能与作用

参考BeanFactoryPostProcessor方法注释可知：该方法是在所有bean被加载，未被实例化前执行。对所有bean的属性可以修改也可以添加

@FunctionalInterface
public interface BeanFactoryPostProcessor {
 
	/**
	 * Modify the application context's internal bean factory after its standard
	 * initialization. All bean 
     
     definitions will have been loaded, but no beans
	 * will have been instantiated yet. This allows for overriding or adding
	 * properties even to eager-initializing beans.
	 * @param beanFactory the bean factory used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
 
}

使用案例

用户可以自定义一个实现BeanFactoryPostProcessor的类，获取某个bean修改bean的属性，比如如下举例修改该UserService类的属性由单例改为原型

 
@Component
public class UserService {
	private String name;
 
	public String getName() {
		return name;
	}
 
	public void setName(String name) {
		this.name = name;
	}
}
 
 
package com.cyl.beanFactoryDemo;
 
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;
 
@Component
public class CylBeanFactoryBeanPostProcessor implements BeanFactoryPostProcessor {
	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		BeanDefinition beanDefinition = beanFactory.getBeanDefinition("userService");
		//修改该bean的属性为原型
		beanDefinition.setScope("prototype");
		//添加该bean的属性name默认值为cyl
		MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
		propertyValues.add("name","cyl");
	}
 
}

spring提供的常见BeanFactoryPostProcessor

1.EventListenerMethodProcessor

处理添加了EventListener注解的逻辑，它的原理参见我的博文:

Spring注解@EventListener实现监听原理-CSDN博客文章浏览阅读903次，点赞21次，收藏14次。@EventListener实现原理主要通过EventListenerMethodProcessor和DefaultEventListenerFactory这两个类实现。EventListenerMethodProcessor的作用是识别所有使用eventListener注解的方法DefaultEventListenerFactory将EventListenerMethodProcessor识别出的方法封装成为监听器类以代码new AnnotationConfigApplicationContext为入https://blog.csdn.net/changyinling520/article/details/137205662?spm=1001.2014.3001.5502

2.BeanDefinitionRegistryPostProcessor

功能与作用

BeanDefinitionRegistryPostProcessor,该接口继承了BeanFactoryPostProcessor，拥有修改bean属性的功能，又拓展postProcessBeanDefinitionRegistry方法，通过代码注释理解:允许在bean被加载后，继续添加新的bean

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
 
	/**
	 * Modify the application context's internal bean definition registry after its
	 * standard initialization. All regular bean definitions will have been loaded,
	 * but no beans will have been instantiated yet. This allows for adding further
	 * bean definitions before the next post-processing phase kicks in.
	 * @param registry the bean definition registry used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
 
}

postProcessBeanDefinitionRegistry方法先执行，postProcessBeanFactory后执行。

可以从详见：org.springframework.context.support.PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors(org.springframework.beans.factory.config.ConfigurableListableBeanFactory, java.util.List<org.springframework.beans.factory.config.BeanFactoryPostProcessor>)

使用案例

用户可以自定义一个实现BeanDefinitionRegistryPostProcessor的类，注册OrderService类到spring容器中，并修改它的属性值

1.创建一个不被spring管理的OrderService，内部有UserService属性

package com.cyl.beanFactoryDemo;
 
public class OrderService {
	private UserService userService;
 
	public UserService getUserService() {
		return userService;
	}
 
	public void setUserService(UserService userService) {
		this.userService = userService;
	}
}

2.创建CylBeanRegistryPostProcessor实现了BeanDefinitionRegistryPostProcessor，在postProcessBeanDefinitionRegistry方法内注册OrderService类到容器中，在postProcessBeanFactory中给OrderService添加属性userService

package com.cyl.beanFactoryDemo;
 
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.stereotype.Component;
 
@Component
public class CylBeanRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
	
    @Override
	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
		RootBeanDefinition rootBeanDefinition = new RootBeanDefinition();
		rootBeanDefinition.setBeanClass(OrderService.class);
		registry.registerBeanDefinition("orderService", rootBeanDefinition);
	}
 
    
    @Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
 
		BeanDefinition userServiceBean = beanFactory.getBeanDefinition("userService");
		//修改该userService的属性name默认值为cyl
		userServiceBean.getPropertyValues().addPropertyValue("name", "cyl");
		
		BeanDefinition beanDefinition = beanFactory.getBeanDefinition("orderService");
		//修改该orderService的添加属性userService
		beanDefinition.getPropertyValues().add("userService", beanFactory.getBean(UserService.class));
	}
 
	
}

最终输出结果

public static void main(String[] args) {
 
		// 创建一个Spring容器
		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
		context.register(AppConfig.class);
		context.refresh();
    
		OrderService orderService = context.getBean(OrderService.class);
		System.out.println(orderService.getUserService().getName());
}

spring提供的唯一BeanDefinitionRegistryPostProcessor

ConfigurationClassPostProcessor，这个类扫描所有component,service,import,configuration等注解，加载所有的bean定义到容器内。后续博文会详细介绍它的处理逻辑

总结

    BeanFactoryProcessor是spring的一个拓展点，它的作用时机是在加载完所有的beanDefinition，还未实例化前。可以对beanDefinition进行加工，但是不可以加载beanDefinition。BeanDefinitionRegistryPostProcessor是BeanFactoryProcessor的子接口，增强了功能，既可以对beanDefinition加工，还可以加载自定义的beanDefinition。